A chronic rat system will be developed suitable for electrophysiological investigations of the aging brain, It will have an array of microelectrodes whose lengths are adjustable during manufacture so that the 3-D distribution of the electrode tips can be arranged to match the 3-D architecture of the cortical feature under study. This system will offer a unique opportunity to investigate in behaving rats the effect of aging on cortical information processing in a way not possible with current techniques. In addition to benefiting directly the aging research community, the tools and techniques resulting from Phases I and II will be applicable to many other programs using electrophysiological recordings from awake, behaving rats. Phase I develops the two key components: (1) a technique for making a 0.4-mm pitch microelectrode array structure where the lengths of individual electrodes can be between 0.5mm and 3.0mm, and (2) a 25-channel percutaneous connector. Chronic experiments will verify the biocompatibility of the connector and its fixation technique. Acute experiments will verify that the multielectrode array can record spontaneous neural activity in rat hippocampus. Phase II will optimize and validate the chronic system for implantation in rat hippocampus and demonstrate the relevance of electrophysiological findings in rat hippocampus to the aging process. PROPOSED COMMERCIAL APPLICATION: A chronic microelectrode array system will be marketed that is suitable for implantation in rats to study the electrophysiologic aspects of aging. It will also be marketed to researchers for investigating other cortical processes in rats.